BIEB 166 Lecture 21 (WI13)

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Biol/Ecology, Behavior, & Evol
BIEB 166
James Nieh

Lecture 21 General characteristics of visual signals Two general production methods 1. Reflected light (most commonly used) 2. Self-generated light Fireflies - Use visual signals in order to communicate - Each species has a characteristic pattern - Male produce very species-specific calls - Temporal modulation of light flashing to attract females 1. Photuris - Female pretends to be a female of the other species - When the males of other species trying to draw her attention, he get devoured (quickly eaten) by the female Video Properties of light signals 1. Intensity - Brightness - Rate of photons hitting a unit surface - Phenomenon independent of color, just counting the rate of all photons - Depends on the environment 2. Spectral composition - Hue ○ Dominant frequency ○ Frequency with the greatest intensity - Chroma ○ Saturation (purity) of the dominant frequency ○ When there is only a single frequency, then it is 100% pure ○ Less intense the color, lower the purity ○ How many photons that are reflected as being yellow An analogy with sound might be helpful to think about the difference between hue and chroma. In nature, colors are generally composed of many different frequencies of light just as natural sounds are generally composed of many different frequencies of sound. Hue is the frequency of the brightest component within a color. This is analogous to the dominant frequency, which is the loudest frequency of sound within a call. When we look at a red cardinal, we see red, which is the dominant color frequency, although there are other that are present as well. Chroma is the purity of the dominant frequency. Thus chroma affected by how diluted the dominant frequency is by other colors. For example, if the red male cardinal is a juvenile male or has had a poor diet, its red color will not be as strong, appearing more orange-red or brown-red. Thus one can say that its red chroma is less than that of a mature, healthy male cardinal. (Incidentally, female cardinals prefer males with stronger red chromas.) If you think of sound, the analogy would be a strong single note (high purity and thus chroma) versus a note obscured by noise (other frequencies). 3. Spatial characteristics: patterns - Exploit the patterns on their bodies to create signals 4. Temporal variability - Turn a visual signal/flash on and off Mechanisms of color production - Reflect photons of different wavelengths Selective absorption with pigments Selective absorption with pigments - Chemical compounds whose molecules absorb certain frequencies of light and reflect and transmit others - The eye perceives the color of the reflected light - Animals can collect them from food or produce them biologically - There are very few actual blue pigments ○ In nature, it is
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